1. Field of the Invention
The invention relates to a gradient coil system for a magnetic resonance appliance.
2. Description of the Prior Art
Magnetic resonance technology is a known technique for obtaining images of the interior of the body of an object being investigated. Rapidly switched gradient fields, which are produced by a gradient system, are superimposed in a magnetic resonance apparatus on a static basic magnetic field which is produced by a basic field magnet. The magnetic resonance apparatus furthermore has a radio-frequency system, which emits radio-frequency signals into the object being investigated in order to excite magnetic resonance signals, and which receives the resulting magnetic resonance signals, on the basis of which magnetic resonance images are produced.
In many embodiments, the gradient coil system has an encapsulation, for example composed of synthetic resin, inter alia to achieve a high dielectric strength and high structural strength. In order to produce the gradient fields during operation, currents flow in the gradient coils of the gradient coil system, having amplitudes reaching several hundred amperes and which are subject to frequent and rapid changes in the current direction with rise and fall rates of several hundred thousand amperes per second. The driving voltage for the coil current is up to several kilovolts. In order to cope with the abovementioned high electrical power levels, it is known for the gradient coil system to be cooled during the operation of the gradient coils. For this purpose, for example, a cooling apparatus can be used which transports heat, which is produced by virtue of current flowing in the gradient coils, out of the coil.
For this purpose, German OS 197 21 985 and OS 197 22 211 A1 disclose examples of a cooling device for indirect cooling of conductors in the gradient coil. In this case, a flexible cooling line, which is laid with its sections closely against one another and through which a cooling medium is passed in order to cool the gradient coil, is introduced in a flat carrier, which is then curved in the form of a cylindrical casing for a hollow cylindrical gradient coil system, and which is encapsulated with casting resin.
Another known arrangement for cooling a gradient coil is described in German OS 198 39 987. In this case, a conductor of the gradient coil is cooled directly by passing a cooling medium through an inner cooling channel, which is surrounded by the conductor in the form of a profiled segment conductor.
German OS 198 03 419 discloses an apparatus for stimulation of body tissues by a magnet coil arrangement which can be placed on a surface of a body and which has a latent heat store which passes through a phase transition within a temperature range of between 0° and 50° C., preferably within a temperature range between 180 and 40° C., and particularly within a temperature range between 200 and 37° C.
German OS 198 58 794 discloses a latent heat body with paraffin-based latent heat storage material, which is held in spaces of a base material. Capillary accommodation spaces for the latent heat storage material are formed within the base material, and the base material contains a mineral substance with an open capillary pore structure. The base material may contain diatomaceous earth, for example. The latent heat body can be used for a wide range of tasks in the form of panels, building blocks, granulates or further shapes.